the AppArmor kernel module should be part of the regular Arch linux kernel

No! as Archwiki say in first step:Installation
Kernel:
Install either linux-hardened (4.17.4 or later) or linux-apparmor.
A third option is to compile a #Custom kernel.

So you will need to install one of this kernels, and change bootorder to boot with the right kernel.
And all the other steps wiki gives you… it is not just install something and it runs, you will need to configure boot process to do so .